Objectives: A. Overall objectives of grant AM 16770: 1. To develop and validate new methods for studying the enterohepatic circulation of bile acids in health and disease. 2. To characterize bile acid metabolism in health and selected diseases. 3. To develop new diagnostic tests for altered bile acid metabolism. 4. To explore poorly understood areas of the enterohepatic circulation. B. Goals for the Current Year (1974): 1. Development of improved methodology. a. Development of a multicompartmental model for bile acid metabolism. b. Synthesis of a new tritium label for bile acids. c. Development of a non-invasive technique for measuring bile acid kinetics. 2. Application of a new radioimmunoassay for cholyl conjugated bile acids. a. 24-hour profile of bile acids in healthy subjects, subjects with cholecystectomy, and patients with bile acid malabsorption. b. Definition of the diagnostic value of fasting-state serum bile acids for detecting liver disease. c. Development and validation of a bile acid tolerance test. 3. Characterization of the effect of primary bile acid ingestion on bile acid metabolism and biliary lipid secretion in gallstone patients. 4. Collaborative studies in patients receiving chenodeoxycholic acid for gallstone dissolution. a. Effect of bile acid ingestion on cholesterol metabolism. b. Development of an algorithm for monitoring hepatotoxicity.